1. Field of the Invention
This invention relates to the field of data processing, data transport and data management systems. More particularly, this invention relates to data processing systems which require sequential and local out-of-order access to data values from within a stream of data values.
2. Description of the Prior Art
It is known to provide data processing systems with cache memories to provide local and fast access to frequently used data values. Such cache memories have considerable flexibility in that individual cache rows may typically be mapped to separate areas within the overall memory address space. This flexibility brings with it an associated overhead in terms of circuit complexity and control. Furthermore, cache memories are typically primarily reactive in that, when new data is to be accessed, a cache miss will occur resulting in that data being fetched into the cache memory whereupon it may subsequently be more rapidly accessed.
It is also known to provide data processing systems which need to access data values from within a stream of data values in a relatively predictable manner. Examples of such systems would be ones processing a stream of audio data which is encoded in a known format and which will be accessed in a regular sequence. Another example would be a system for processing a stream of video data in which the images occur in a sequence and are encoded in accordance with a known format which is processed in a regular sequence. It is desirable to provide local high speed access to such streamed data. A generic cache memory used for this purpose would however bring with it a significant amount of associated circuit overhead and complexity which was not necessary since the accessing of the stream data is relatively predictable. Furthermore, traditional cache memories operate on a reactive basis and thus cache misses would occur as new portions of the stream data needed to be accessed with a resulting disadvantageous delay whilst a cache fill took place.